Carbonization at high temperature can significantly increase the conductivity of polyaniline nanofibers (PANF) but the created carbonized surface is too hydrophobic for Pt-loading. Sulfonic acid groups are then grafted on the carbonized PANE by ultra-sonication in concentrated sulfuric acid to increase the surface hydrophilicity and Pt-loading. The obtained sulfonated carbonized PANF was found to own not just high conductivity but good hydrophilicity which can load more than 18% of Pt on the surface from a 25% H2PtCl6(aq) and demonstrate better electrochemical activity in the cyclic voltaic and ORR testing. The surface area of the loaded Pt per unit support can be increased from 85.66 to 276.61 cm(2) mg(-1) after 24 h of sulfonation. The single cell performance demonstrates an increasing power and maximum current density with degree of sulfonation for MEA made of the sulfonated carbonized PANE. (C) 2014 Elsevier Ltd. All rights reserved.